Centralized traffic controlling system for railroads



N. D. PRESTON Aug. 18, 193.

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CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Original Filed Dec. 29, 1932 '7 Sheets-Shet 2 At wul N? +v u @N\ 3\ I m 31 n m n m n u n m E 2 a mu Kw I w J; 52 Pm: a v I 1/ Nv kw r w 2: llwfi 3m Mk I IN Aug. 18, 1936. N. D. PRESTON- CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Original Filed Dec. 29, 1932 7 Sheets-Sheet 3 Original Filed Dec. 29, 1932 CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS NQN Aug. 18, 1936.

0 m if Aug. 18, 1936. N. D. PRESTON 2,051,419

CENTRALIZBD TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Original Filed Dec. 29 1932 7 Sheets-Sheet 6 Kg om 2 w: m m

Patented Aug. 18, 1936 PATENT OFFICE CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Neil D. Preston, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

Application December 29, 1932, Serial No. 649,369 Renewed November 21, 1935 17 Claims.

This invention relates to centralized traflic controlling systems for railroads, and more particularly to the communication part of such systems.

The system of the present invention is to be considered an improvement on my earlier filed copending applications Ser. No. 589,186, filed January 2'7, 1932, and Ser. No. 644,481, filed November 26, 1932.

In railroad trafiic controlling systems, the traffic is controlled from a control oifice usually located at a central point with respect to outlying field stations, which are connected to the control ofiice by means of the communication system. Likewise, the location of trains and the condition of the traffic controlling devices at remote locations or outlying field stations are indicated to the attendant at the control office. The location of trains and the condition of the traific controlling devices are transmitted to the control ofiice by means of the communication part of the system. This invention is particularly useful in such a system which is called upon to carry out a large number of controls and indications during a very short time. A single dispatcher can handle the trafiic over a large section of track so that it is desirable that the code combinations be capable of transmission at such a high rate of speed that the accumulation of stored controls and indications is avoided.

The switches and signals are distributed throughout the territory and those located relatively near or adjacent each other, together with the apparatus provided to govern these switches and signals, are conveniently referred to as comprising a field station. The communication system is provided to interconnect the control office with the several field stations and is so organized that complete control and supervision of the various switch and signal devices at the remote stations are obtained by the operator. Such a traflic controlling system is supplemented by the well known automatic block signal system and other local means ordinarily provided to guard against unsafe train movements. improper operation of track switches or the like.

In accordance with the present invention, the communication system comprises three line Wires extending from the control office through the several field stations in series. These three line conductors are referred to in this disclosure as the S line, which is the stepping line and the A and B lines, which are the return conductors. The S line, in addition to being used for controlling the stepping operations, is used in com:

bination with the A and B lines for the transmission of controls from the control ofiice to the field stations. The S line, likewise, cooperates with the A and B lines in connection with the transmission of indications from the field sta- 5 tions to the control oflice.

The S line and the A and B lines are connected together at the last field station of the series and the circuits are so organized that current which is applied to the S line at the control office 10 extends through the several field stations in series and at the last field station, a return path is completed by way of the A and B lines. The arrangement is such that any field station in the series may control the circuits in a manner 15 that the return path to the control ofiice may be by way of one or the other or both the A and B line conductors.

In accordance with the present invention, it is proposed to use the three line wires for trans- 20 mitting codes for selecting one particular field station at a time and actuating controlling devices thereat. Likewise, these three line conductors are used for transmitting'codes for registering one particular field station at a time in the 25 control ofiice and thereafter actuating certain indication devices at the control office associated with the registered field station.

The system is of the coded simplex type and is operated through cycles during each of which either the transmission of controls or the transmission of indications can occur. The communication system is used for the transmission of controls and indications in such a way that, irrespective of the number of stored controls in the control ofiice awaiting transmission to field stations, a field station may be registered in the control oifice and cause the next succeeding operating cycle to be anindication cycle. If s ev-, eral controls for transmission from the control office to field stations are stored and several indications for transmission from field stations to the control office are stored at the same time, the system operates in such a way that controls and indications will be transmitted during alternate cycles.

For the transmission of controls, a predetermined number of impulses of selected polarities is placed on the line circuit for operating the apparatus at the control ofiice and at the field stations through a cycle of operations, irrespective of the character of the impulses. The distinctive character of these impulses in part determines the particular station to be selected and the controls to be transmitted to the selected station. In addition to the character of the impulses applied to the S line, the circuits are so organized that the return path from the field stations may be by way of both the A and B line conductors in multiple or the B line conductor alone. This provides means in addition to the polar impulses for the transmission'o'f controls so that a choice of four code combinations is obtained for each step.

For the transmission of indications, meansare provided to condition the A:and -]3 lines during a portion of each energized period of the S line for creating two code characters, either one of which may be selected. During another portion of each energized period of the S line, the A'and B line Wires are again conditioned to provide a choice of three code characters, any one of which may be selected. Therefore, a choice of five code characters for each step is obtained during each energized period of the S line circuit. The energized periods of the S lin'e circuit will be referred to as the on periods, while the deenergized periods of the line circuit will'be referred to as the off periods. 7

{Oneifeature 'of the present invention relates to the manner in which indications are precondi- "tion'eddurlng the oif periods, for obtaining a choice of two codecharacters and conditioned during the 'on periods for obtaining an additional choice of three code characters, with the chosen indications executed during a "portion of an on period and a portion of the next sue-- ce'eding off period.

In the presentembodiment, with the S line energized at the start of an on period, the A or B line may be energized, resulting in'two distinctive conditions. With the Sline energized later during the same on period, the return circuit may be by 'wayof the A line alone, the B line 7 alone or the A and B lines in multiple, thus giving three more distinctiveconditions, thus resulting in five separate and distinct conditions or code'combinations for each step for thetransmission of indications.

Another feature of the present invention 'relates to the manner in which controls are conditioned during thebfi periods, for obtaining a.

choice of four codecombinations and the manner in which the chosen controls are executed during the next succeeding on period. Obviously, the

provision of four distinctive code combinations for eachstep results in obtaining 'sixteendi'stinctive codes where each complete code comprises two steps. Similarly, sixty-fourdistinctivecomplete codes are obtained where each "complete code comprises three steps. In other words, the.

numberof code combinations for the transmis- -sion ofcontrols is-equal tofourraised to the power ftwo st'eps.

code cornbinationsobtained is equal to five raised to' the power-of the number of steps and this is accoinplished by'energizing the line circuits-with of the number of steps. This is accomplished by energizing the line-circuits with current of different polarities and. providing the return path current of the same "polarity for eachdis'tinctive code.

Y 'I'herefore, one purpose 'of the present invention is to provide a code type selector "system and MB, respectively, in the control ofiice.

which builds up rapidly as the number of steps increases and to accomplish this over a minimum number of line wires. I

Other objects and. advantages of the present invention will be hereinafter setforth in the specification and claims and further details will be better understood by referring tothe accompanying drawings, which illustrate one method of carrying out the invention by way of example.

The drawings illustrate in a diagrammatic manner the apparatus and circuits employed and for'convenience in describing the invention in detail, those parts having similar features and functions are designated in the different figures by like reference characters, generally made distinctive either by the use of distinctive exponents representative of their location or by the use of suitable preceding numerals representative of the order of their operation, and in which:

Fig. 1 diagrammatically shows the line circuits illustrated in Figs. 2A, 2B, 2C, 2D and 3.

Figs. 2A, 2B, 2C and 2D illustrate the apparatus and circuits employed at the control office;

Fig. 3 illustrates the circuits employed at one of the field stations;

Fig. *4 illustrates an operation chart which will be conveniently referred to during the following description for obtaining a concentrated picture of the sequence of operations of the system during control and indication cycles;

:Fig. 5 shows a modification of the line circuits.

To simplify the line circuit schematic, Fig; 1 shows the line condition after a cycle is started, rather than its normal at-rest condition.

When tracing the circuits, Figs. "2A and 23 should be placed together in the order named, Figs. 2C and 2D should be placed together in the order named and below Figs. 2A'and 2B with correspondingly numbered lines in alignment.

Gener'al description The three-wire line'circuit which connects the control office with the field stations is shown in heavy lines. Fig. "1 indicates, in schematicform, the three line conductors and shows the S line with battery connected to it from'battery B, through the windings of relay F in the control ofiice and relays F F, F etc. at the field stations. At the last field station of the series, theS line is connected through resistance coils R and R to the A and B lines respectively. In series with the A'line at 'the stations'are A line relays FA FA FA etc., as well as'contacts of the A line impulsing relays at the stations, such as PLA PLA PLA etc. 1

The embodiment shown in Figs. 2A, 2B, 2C;

and 2D does not have resistance coils RS RS RS etc., nor the contacts shown in connection with relays S0 S0 SO ,-etc., of Fig. 5 so that the :A line conductor at'the different stations is in series with only the A line relays and the con-' tacts of the A line pulsing relays. The 13. line conductor is in series with the B line impulsing contacts such as 'PliB PLB PLB etc., while both the A'and B line conductors are connected in series with A and B line message relays MA Contacts of relay PCA in the control oiiice are used to open and close the A line in a manner and for a purpose which will be specifically pointed out in detail.

The dotted rectangle in the upper right hand portion of Fig. 3 shows the extension of the 5 line through line relays of other'field stations and the connection to the A and B return conductors through resistance coils at the last station and contacts of the A and B line impulsing relays at other stations.

It will be understood that stations in addition to the one shown in Fig. 3 have apparatus and circuit arrangements practically the same as that illustrated. As will be more specifically pointed out in the following description, the points of difference in the circuit connections at different field stations are the distinctive connections of the code jumpers for conditioning the circuits so that a particular field station will'be fully responsive only to the particular code assigned to that station.

The symbols and indicate the positive and negative terminals respectively of suitable batteries or other sources of current and the circuits connected to these symbols always have current flowing in the same direction. The symbols (13+) and (B) indicate the positive and negative terminals respectively, of a battery or other source of current having an intermediate tap (CN) and the circuits connected to these symbols, may have current flowing in one direction or the other, depending upon whether the circuit connected to terminal (3+) or (B) is completed to the intermediate tap (CN) No attempt has been made to show all of the apparatus employed, such as the total number or" manual controlling devices at the control office, the total amount of equipment or its exact arrangement at the field station, since this apparatus and equipment may vary in extent to suit local conditions. The character of the apparatus illustrated in the typical control office and the typical field station will now be considered.

Control ojfice equipment.-As typical of the equipment located in the control office, a control machine having a group of control levers for each field station connected to the line circuit is provided. A miniature track switch ts corresponds to a particular track switch in the field and represents the actual track layout at the field location. Various indicating lamps or equivalent devices are likewise provided, with apparatus and circuit connections arranged to control these indicating devices as required.

The equipment for one track switch comprises a switch machine lever SML, a signal lever SGL, a self restoring starting button SB, a miniature track switch is and the indication lamp OS. Similarly, additional control levers (not shown) may be associated with a single field station, but in order to simplify the drawings and description, these devices have been omitted. Additional indicating devices, such as signal lamp OS, may likewise be provided but they have not been shown in this embodiment for the sake of simplicity. The selection of the field station illustrated in Fig. 3 by means of starting button SB of Fig. 2A and thereafter the control of a track switch TS (Fig. 3), by means of a lever SML (Fig. 2A) may be considered as typical of the selection of other field stations and the control of other traffic controlling devices. Likewise, the registration of a field station by means of an automatic start from the field and thereafter the transmission of indications from track relay T (Fig. 3) may be considered as typical of the registration of other field stations and the transmission of other indications.

The actuation of the lever SML to one extreme position or the other, followed by the depression of the starting button SB, results in the normal or reverse operation of the track switch corresponding to lever SML at that field station which is associated with starting button SB and this operation is controlled through the medium of the communication system of the present invention. The momentary depression of the starting button is preferably stored by a storing relay (not shown) which in turn picks up the corresponding code determining relay CD of the associated station. The starting button SB is shown connected to relay CD by means'of a dotted line instead of the complete circuit connections, in order to simplify the present disclosure.

The storing relays associated with the starting buttons and their corresponding CD relays are so interconnected that only one CD relay may be up during one cycle of operations, irrespective of the number of storing relays which are simultaneously energized or energized in rapid succession. This interconnection of the CD relay circuits is so arranged that if several storing relays are up at the same time, the corresponding CD relays will be picked up one at a time during successive operating cycles, in an order predetermined by their relative locations in the relay bank, all of which has been completely disclosed in the prior application of N. D. Preston et al., Ser. No. 455,304, filed May 24, 1930.

The control oflice includes a selecting relay SEL which responds to the polarity of the conditioning impulse applied to the S line. picked up at the start of an indication cycle, remains up until the end of the indication cycle and stays down during a control cycle. Its function is to select the control and indication circuits during control and indication cycles. A control ofiice start relay C is picked up when a cycle of operations is initiated from the control office and a field start relay PC is picked up when a, cycle of operations is initiated from a field station. Either relay C or relay PC when picked up,is stuck up through back contacts on an extra stepping relay LV in combination with contacts on relay SEL, so that relay C will drop at the end of a control cycle while relay FC will be held up. If relay FC is up, relay C cannot pick up.

The circuit connections of relays C and F0 are such that when indications and controls are stored in both the field and the control ofiice, the control ofiice has the preference in obtaining control of the line circuit so that the first cycle will be a control cycle. The next cycle will be an indication cycle and if several controls and indications are simultaneously stored, the communication system will be used alternately for controls and indications.

Line relay F and line repeating relay FP are used to control the stepping and selecting operations. Slow acting line repeating relays SA and SAP are picked up at the beginning of each cycle and dropped during the change to normalperiod at the end of the cycle. These two relays have such slow acting characteristics that the pick-up time of each is relatively long compared with the pick-up time of relays such as F and PP. 'The pick-up time of these slow acting relays is relatively short in comparison with the time required for their release after they are de-energized by the removal of current from their windings. The releasing or drop-away time of relay SA is sufiiciently long so that its contacts remain in their actuated positions during all off periods between successive impulses of a cycle, but these contacts are restored to normal during the last off period, which is comparatively long This relay is for thepurpose of returning. the system to the normal period of rest or the period of blank.

Associated with line relay F and its repeating relays is a bank of stepping relays IV, 2V, 3V and LV together with a half step or steering relay VP, which are provided to mark oil? the a successive steps of each cycle. Steering relay VP serves'the purpose of steering the impulses from relay FP to the proper stepping relay and for steering the executing circuits to the proper selecting contacts of the stepping relays, all at the V proper time. An impulsing relay E is jointly con- 'ing relay EP, jointly controls with relay FP, the

stick circuit 'of relay MX. Relay E also controls the stick circuit of relays MAP and MBP as well as controlling the circuits over which the P indications are executed, all of which will be specifically pointed out in the detailed description. Relay MA is controlled'over the A line conductor, relay MB is controlled over the 13 line conductor and their respective repeating relays MAP and MBP control the selection of a choice of five indication code combinations during the on period of each step. Relay MX is jointly controlled by relays MAP and MBP to record the choice of two of these indication code combinations during the first part of the on period of each step. Relays MAP and MBP thereafter record the choice of three of these combinations during a succeeding part of the on period of each step.

The polarity of the impulses applied to the line circuit from a battery B is determined by positive code sending relay PC and negative code sending relay NC. These two relays are controlled on steps of a control cycle in accordance with the station code and the controls to be transmitted for that particular cycle. A line con-' ditioning relay PCA is provided for energizing or cle-energizing the, A line conductor during the transmission of control impulses. Relays PC, NC and PCA in combination provide a choice of four distinctive control code combinations for each step. A starting relay STR is picked up to initiate a cycle of operations, both when controls are to be transmitted due to the manual initiation' of the cycle in the control ofiice and when indications are to be transmitted due to the.

understood that any othersuitable type or arrangement maybe provided for accomplishing the result obtained by this typical arrangement.

A station relay ST (Fig. 20) provides for the registration in the control ofiice of the station which is transmitting indications.

This relay is merely typical of a number of such relays which would ordinarily be provided, one for registering each individual station. The other relays,

illustrated in Fig. 3, as repeated by a track relay T so that indicatinglamp OSis controlled by the passage of a train to visually indicate to the dispatcher theoccupied or unoccupied condition of the section of track. It will be understood that relay IR is merely typical of additional indication storing relays which may be provided for storing additional indications repeated by other conditions at the field stations, such as the posi-' tions'of switch'machines, signals, etc.

Field station equipment-The field station illustrated in Fig. 3 includes, besides the apparatus already mentioned, a quick acting line relay F and a quick acting line repeating relay FP which repeat the energizations and deenergizations of the S line circuit. Relay FP repeats the impulses in the S line circuit irrespective of their polarities while relay F is actuated to the right by a positive impulse and to the left by a negative impulse applied to the line from battery B in the control oflice.

A slow acting relay -SA of the neutral type repeats the energized condition of relay FP having such characteristics that its pick-up period is long compared with the pickup period of a fast acting relay such as FP The releasing pcriod of relay SA is relatively long compared with.

associated steering or half step relay VP operating in a similar manner and in synchronism with the stepping relay bank in the control ofiice. Steering relay VP steers the impulses from relay FP to the proper stepping relay, as well as steering the connections from the windings of the line impulsing relays PLA and PLB to the proper indication buses, .all at the proper time.

The line impulsing relays PLA and PLB function to open theA and B lines respectively, to provide code combinations during the transmission of indications. These two relays are conditioned in accordance with the condition of the indication buses shown in the lower right hand portion of Fig. 3. Relay VPC exercises a control over the steering relay VP in such a way that relay VP cannot shift until the line impulsing relays PLA and'PLB are in their normal or deenergized positions during the on periods.

A change repeating relay CHP is provided to' register a change in the trafiic controlling devices at the station, so that the system will be automatically started through .a cycle of operations for the transmission of new indications whenever this relay is down. Although the circuit of relay CHP is not shown in detail, it will be understood that it is normally stuck up and is released to close its back contact I51, by the interruption of its holding stick circuit (not shown), when a change in position of a track relay T or any other suitable relay takes place. Relay CHP will register a change in one or more of a large number of devices and initiates indication cycles as long as there are new indications to be transmitted.

A lock-out relay L located at each field station, determines when a particular station is to transmit new indications. This relay is picked up during the initiating period of an indication cycle and is stuck up until the change to nor mal period at the end of the cycle. The lock.- out relay supplies potential to the A and B line impulsing relays PLA and PLB as long as the station relay S0 is down, so that these line impulsing relays receive current during an indication cycle only at the station transmitting indications.

A station selecting relay S0 is provided at each field station and picks up at all stations during the conditioning period of a control cycle. These station selecting relays are dropped out at various stations during the transmitting period of a cycle, so that only the one associated with the desired station remains actuated after'the transmission of the station selecting code. Relays L0 and S0 control the circuits to the stepping relays so that stepping is not effected at those stations not in connection with the communication circuit.

An additional line relay FA is included in the A line circuit and is used in cooperation with line relay F for repeating the code combinations transmitted during a control cycle, for performing selective and control functions as will be specifically pointed out in detail. Resistance units R and R illustrated within the dotted rectangle in the right hand portion of Fig. 3, are inserted in the A and B line conductors at the last station of the series to provide a drop in potential for picking up a lookout relay, similar to relay L0 during the initiating period of an indication cycle.

A track switch TS is operated by a switch ma-- chine SM of any suitable type, such for example, as disclosed in the patent to W. K. Howe, 1,466,903 dated September 4', 1923. The position, locked and unlocked conditions of the track switch are repeated by the usual switch repeating relay (not shown). The track switch has associated with it the usual detector track section, having a track battery and a track relay T as well as suitable approach l'ocking and detector locking means to govern the safe operation of the track switch, in accordance with traffic conditions.

A change in the condition of the detector track section is repeated by relay T and the circuits used for transmitting the condition of relay T have been shown in detail, The indication code circuits which are connected to contacts of relay T may be considered typical of the manner in which other indication code circuits are connected to other relays, such as the relay which respondsto the operation of the track switch.

It is believed that the nature of the invention, its advantages and characteristic features may be best understood by continuing the description in a manner relating to the operation of the system.

General operation The circuits are shown in the normal or condition of rest, from which the system may. be

initiated into a cycle of operations by a manual.

operation at the control oflice or an automatic operation at any one of the field stations, whenever there are new controls or new indications, respectively, to be transmitted.

Irrespective of whether a cycle is for the transmission of controls or the transmission of indications, a predetermined number of impulses is applied to the line circuit to cause the stepping relays at the control oflice and at the field stations to operate in synchronism. These impulses are of comparatively short duration, the de-energized or 0!? periods of the stepping line circuit being comparatively shorter than the energized or on periods, except the last off period which is suiiiciently long to allow the slow releasing relays to release for restoring the system to normal.

When a cycle of operations is initiated for the transmission of controls, the character of the impulses applied to the stepping line and the condition of the A line return conductor are determined by the particular station to be selected and the particular controls to be transmitted to the selected station, in accordance with the code jumper connections and the positions of the control levers, respectively, for that station.

During the transmission of controls, the A and B line conductors are energized in multiple and in series with the S line conductor at each step under certain conditions and under other conditions the B line conductor alone is energized in series with the S line conductor at each step. During the transmission of controls, an initiating impulse is applied to the S line conductor for picking up all the station relays similar to relay S0 of Fig. 3. 7

When a cycle of operations is initiated for the transmission of indications, the character of all impulses applied to the stepping line is the same, with the A and B lines conditioned as determined by the indications to be transmitted from the field station. The initiating impulse applied to the stepping line is which is effective to prevent picking up any station relay similar to S0 of Fig. 3. Since the line circuit is energized with a series of impulses during such a cycle and since the cycle starts out with no station relays similar to S0 picked up, the impulses which follow the initiating impulse are inefiective to select a station or actuate a control device at a station.

The A and B line conductors are normally energized, the stepping line conductor S is normally deenergized and when controls or indications are initiated, the battery connection in the control oifice is switched so that temporarily the S line is energized, the return circuit being by way of both the A and B lines, for the transmission of controls and by way of the B line alone for the transmission of indications,

This period during which the battery is switched from the A and B line conductors to include the S line is conveniently referred to as the conditioning period at the start of a control cycle and the initiating period at the start of an indication cycle. Immediately following the conditioning or initiating period is the look-out period, effective during an indication cycle to so condition the circuits that only one station may transmit indications at the same time.

After the conditioning and lock-out periods, the system continues through a complete cycle of operations, consisting of a number of oif and on. periods, this number being determined by the number of steps required and the number of steps in turn being governed by the size of the system. After the last on period, a comparatively long off or lie-energized period is provided to condition the. relays for changing to normal or the period of blank. After this change to normal period, the A and B line conductors are again energized by current from battery B, which restores the system to the normal period. 7 For convenience in describing the operation of the present invention, an operation chart is shown in'Fig. 4. In the upper portion of this chart, the important functions during acontrol cycle are illustrated, while the lower portion illustrates the important operations of an indication cycle. Referring to the control cycle, the normal period is shown at the extreme left and during this period line S is de-energized or open as indicated by reference character 0. Line A is energized with potential and line B with potential as indicated. It is during this period that the system is manually started from the control ofiice. The normal period is an off period since line Sis de-energized.

During the next or conditioning on period, line S is energized with potential and the return circuitby way of lines A and B is to() potential, as indicated by these referencechar- ,periodswith only three steps indicated, namely, a the first, second and third oil and ,on.

serted between the, third ,on and the change to It will be understood that additional steps are innormal periods when the, size of the system increases. In the indication cycle chart of Fig. 4 a normal period is shown which is the same as the control cycle normal period, except it is noted that this cycle is started automatically from the field. This is followed, by an operating cycle divided into initiating, lock-out, conditioning, transmitting and change to normal periods.

The conditions of the line conductors during these different periods and certain important relay operations are set forth in the different columns of this chart. The transmitting period, in addition to being divided into oil and .on periods,

. has these periods subdivided as indicated, the

purpose of which will be specifically described.

Detailed operation 7 Normal periodRelays MA and MB are normally energized by current flowing over the A and B lines in series and extending from the terminal of battery B, back contact II) of relay STR, back contact I5 of relay PCA, conductor I6, winding of relay MA, A line conductor II,

back contact I50 of relay PLA winding of relay FA conductor I5 I, through contacts such as PLA and windings of relayssuch as FA at other field stations, resistance coils R and R in series at the last field station, back contacts such as PLB at other field stations, conductor I52, back contact I53 of relay PLB B .line conductor I2, winding of. relay MB, conductor I24 and back contact I3 of relay STR tothe terminal of battery B. Relay MAP is normally energized over a circuit extending from front contact I28 of relay MA and lower winding of relay MAP, to Relay MBP is normally energized over a circuit extending from front contact I29 of relay MB and lower winding of relay MBP, to

(-). All other relays in the control oflice are normally de-energized.

In pointing out the relays which are normally energized at the field stations, it will be understoodcthat relays similar to those shown in Fig. 3 are normally picked up by means of circuits described in connection with this figure. Relay VPC is normally energized over a circuit extending from back contact I90 of relay PLA back contact I95 of relay PLB and winding of relay VPC to 1 Change repeating relay CHP and track relay T are normally picked up over circuits (not shown), but obvious to those skilled in the art.

mal condition it will be assumed that the operator in the control oifice desires to send controls to a particular field station, such as the one illustrated in Fig. 3. It will be assumed that the complete code associated with this station is and that it is transmitted during two off and on periods, marked err by the operation of the first two stepping relays. The code jumper connections at the control .ofiice and at the field station have been shown connected in accordance with this particular distinctive code. It will also be assumed that the distinctive code sent out from the control ofiice during the third step is determined by the positions of levers SML and SGL.

When the starting button SB is actuated, a suitable storing relay is operated and its associated CD relay, which corresponds to the station associated with button SB, is ,picked up. When relay CD picks up, it closes a circuit for picking up relay C which extends from back contact l6 of relay SA, conductor I36, front contact H of relay CD, conductor I31, back contact 23 of relay FC and winding of relay C, to .fRee lay C closes a stick circuit for itself extending from back contact 24 of relay LV, conductor I38, front contact 68 and winding of relay 0, to

The operation of relay C opens, at its back contact 14, the direct circuit to relay NC so that the operating circuit for relay NC is by way of the code jumper connections alone. Relay C closes a circuit for picking up relay S'I'R which extends from back contact 32 of relay SAP, front contact I8 of relay C and windingof relay STR, to Relay C also closes a circuit for picking up relay PC which extends from back contacts I9, 20 and 2I in series of stepping relays 3V, 2V and IV respectively, conductor I39, front contact 22 of relay C and lower winding of relay PC, to

Th-isis the conditioning period. The picking contact 2-! of relay EP, Sline conductor 28,, winding of relay F of the field station shown in Fig. 3,

windings of other line relays similar to F located at other field stations, resistance coil R at the last field station, windings of relays such as FA at other field stations, back contacts such as PLA at other field stations, conductor I5I, winding of relay FA back contact I50 of relay PLA 7a A line conductor II, winding of relay conductor I6, back contact I5 of relay PCA, front contact I3 of relay STR, back contact I of relay NC and front contact 8 of relay PC to the terminal of battery 13. This circuit .branches off at the last field station and also extends through resistance coil R back contacts similar to PLB at other field stations, conductor I52, back contact I53 of relay PLB B line conductor I2, winding of relay MB, conductor I24, back contact I of relay NC and front contact 8 of relay PC to the terminal of battery B.

The above described circuit energizes line S with a potential and lines A and B in multiple with a potential, as indicated under the conditioning period in the operation chart of Fig. 4. This current actuates relays F, F and other relays such as F to the right. Relays such as FA relay FA relay MA and relay MB remain in their actuated positions. Relay F closes a circuit for picking up relay FP which extends from contact 29 of relay F in its right hand position and winding of relay FP, to Relay F closes a circuit for picking up relay FP which extends from contact I54 of relay F in its right hand position and winding of relay FP to The actuation of. relay FP in the control office closes a circuit for picking up relay SA which extends from front contact 38 of relay FF and winding of relay SA, to Relay SA closes a circuit for picking up relay SAP extending from front contact 3| of relay SA and winding of relay SAP, to

At the field station, a circuit is closed for picking up relay S0 which extends from back contact I58 of. relay SA back contacts IBI, I62 and I53 of relays 3V 2V and IV respectively, contact I50 of relay F in its right hand position and winding of relay S0 to It will be understood that a similar circuit is effective at other field stations for picking up other relays similar to S0 7 The actuation of relay FP closes a circuit for picking up relay SA which extends from front contact I55 of relay PP and winding of relay SA to The operation of relay SA interrupts the above described pick-up circuit of relay S0 but it is not;released, since aholding stick circuit is closed extending from front contact II'I of relay S0 back contacts IBI, I52 and I 63 of relays 3V 2V and IV contact iGil of relay F in its right hand position and winding of relay S0 to Referring back to the control oflice, the actuation of relay SA closes a stick circuit for holding relay STR in its picked up position until the end of the cycle, which'circuit extends from front contact I6 of relay SA, front contact 38 of relay STR and winding of relay STR, to This stick circuit is closed before the pick-up circuit of relay STR is opened at back contact 32 of relay SAP. Relay SAP opens, at its back contact 69, the pick-up circuit of relay FC so that this latter relay can not pick up toregister a field station start until the system is advanced into its normal period by the release of relay SAP.

Relay SAP closes a circuit for picking up relay EP which extends from front contact 32 of. relay SAP, back contact 33of relay E and lower winding of relay EP, to The purpose of front contact SI of relay EP is to short circuit the upper winding of this relay after it is picked up, which has the effect of-rendering it quick to pick up and slow to release, which is desired for the proper timing of the stepping operation. The actuation of. relay EP opens the S line conductor at its back contact 21, which is effective to deenergize the line circuits and advance the system into the first off period.

Polarity selection of impuZses.As above pointed out, the first impulse in line S is when a cycle of operations is started from the control office and is due to the fact that control relay PC is picked up at the start of a control cycle. This impulse, in addition to the above mentioned operations, fixes this cycle as a control cycle by preventing the picking up of relay SEL of Fig. 2B, because contact 39 of relay F is not closed before back contact 3| of relay SA is opened.

With line S de-energized and the system in its first off period, relays F, F and others such as F are released. Relay F causes the release of relay FP by opening its contact 29. As will be specifically pointed out later on in the description, stepping relay IV is picked up during the first off period. The No. 1 control is conditioned by selecting the polarity, during the first off period, to be applied to line S during the first on period. Assuming that relay IV is up, a circuit is effective for energizing relay PC which extends from back contact 40 of relay SEL, conductor Mil, back contact 35 of relay 3V,

back contact 36 of relay 2V, front contact 3'! of relay IV, No. 1 code bus 44, front contact of relay CD, code jumper 43, bus 41 and lower winding of relay PC, to This connection of code jumper 46 to bus 41 selectively conditions the first part of the first control impulse If code jumper 46 were connected to bus 42, then relay NC would be picked up instead of relay PC, thus providing a impulse for the first part of the No. 1 control.

The second part of the No. 1 control is determined by the condition of relay PCA and in the embodiment disclosed it is assumed that relay PCA is down during the first o period. This results in both lines A and B becoming energized in series with the S line during the first on period,- because contact I5 remains closed.

If code jumper 45 is connected to the second terminal from the bottom leading to code bus 4|, relays PC and PCA are both picked up in series, the circuit extending through the upper winding of relay PC from bus 4| and the lower winding of relay PCA, to This provides a impulse on the S line for the first part of the No. 1 control code because relay PC is up. Relay PCA up establishes the return circuit by way of the B line conductor alone, since back contact I5 is open, which opens conductor I3 leading to the A line conductor II.

With the A line conductor energized (when code jumper 46 is connected to the lower terminal leading to bus 41), relay FA at the field station picks up. The energized condition of the A line conductor is conveniently referred to as a code and is indicated thus in the second part of the code in the first o and on periods of the control cycle shown in Fig. 4. If the A line conductor is de-energized, then relay FA is down and this is conveniently referred to as a code combination.

It will thus be seen that four distinctive combinations are obtained during each step when controls are transmitted. These are: First, with jumper 46 connected as shown in Fig. 2A, which results in relay PC being up, relay NC being down'and relay-PCA being down. This results in energizing line S and energizing line A for picking up relay FA Second, a combination is obtained when code jumper 46 connects to the second terminal from the bottom leading to bus 4 i, because relays PC and PCA pick up. Relay PC energizes line S and relay PCA de-energizes line A, which is conveniently referred to as Third, a combination is obtained when jumper 46 is connected 'to the third terminal from the: bottom, which leads to bus 42 and is effective to pick up relay NC alone. Relay NC energizes line S and since relay PCA remains down, relay FA picks up which is referred toas Fourth, a combination is obtained when jumper 46 is connected to the fourth terminal'from the bottom leading to bus II, since this results in picking up relays NC and PCA in series. Relay NC energizes line S and relay PCA opens the A line conductor so that relay FA remains down which is referred to as a The control of the PC, NC and PCA relays is similar during other off periods by means of other code jumper connectionssuch as 61. Thus, in theflsecond off period relays 2V and VP will be up and the selection of the or combinations by means of jumper 61 selectively connected to one of the bus wires 41, M, 42 or II, is extended byway of front contact III of relay CD, No. 2 code bus H2, front contact 36 of relay 2V, back contact of relay 3V, conductor I and back contact 40 of relay SEL, to In the presentembodiment, it is assumed that the second step (No. 2) code jumper 61 connects to bus II, so that relays NC and PCA will be up during the second off period. With relays NC and PCA up and relay PC down, the code combination is asabove explained and as is indicated in Fig. 4. a During the third oif period, it will be assumed thatrelay 3V is up, as indicated in the operation chart. The No. 3 control is conditioned during this period by extending the circuit from back contact 40 of relay SEL, conductor I40, front contact 35 of relay 3V,.No. 3 code bus II 4,'front contact l I5 of relay CD, Contact 43 of lever SML in its right hand position, bus 41 and lower winding of relay PC, to This determines the first part of the No. 3 control The second part of the No. 3 control is ,determined by picking up relay PCA over a circuit which extends from back contact I I6 of relay SEL, conductor I4I, front contact N1 of relay 3V, front contact H8 of. relay CD, contact II9 of lever SGL in its right hand position, bus I25 and upper'winding of relay PCA, to

It will be apparent that a impulse would be conditioned for the first part of the No. 3 control if lever SML should be in its left hand position,

because this would extend the first part of the above traced circuit through contact 43 of lever V SML in its left hand position to bus 42, which would be efiective to energize relay NC. Likewise,

' if lever SGL were in its'alternate position, contact H9 would be open so that bus I25 would be deenergized and relay PCA would be down for making the second portion of the No. 3 control code because this'would result in picking up relay FA at the field station. 7 1

From the above it will be observed that different code combinations in groups of two per step and a choice of. four per step may be chosen for selecting different stations, by arranging the jumper connections 46 and 61 in different positions. It

will be obvious that sixteen combinations may be obtained with these two jumper arrangements for two steps and if an additional jumper is provided for the third step, sixty-four combina tions are obtained It will also be understood 5 that more than one step may be provided for selecting additional control devices similar to levers SML and-SGL and that the positions of two such devices maybe repeated for each additional step provided. 10

It is believed that the typical arrangement shown and described is suflicient to illustrate the complete functioning of the system with respect to the provision of code combinations. It will be seen that the impulses applied to the line 115 circuit during a control cycle always begin with a and a combination of and im-' pulses in line S follow, with line Aeither energized or de-energized in combination with line B for the return circuit.

These following impulses and the condition of conductor A are dependent upon the code jumper connections and the control lever positions made effective by-the particular code determining relay 4. CD which is picked up during the control cycle. 2'5 Also, the character or polarity of the impulses in line Sis selected by polarity determining relays PC for a and NC for a and the condition of the A line is selectively determined by relay PCA being down for a and up for a 30-:

referring to the condition of relay FA at the field 315 T station. The polarity of the impulses, as well as the condition of the A line return conductor are determined during the off periods in readiness for the application of the preselected codes during the following on periods. 7

' Line pulsing and'operation. of stepping relays. It has been explained that line S is normally deenergized and is energized during the operating cycle with polar impulses. Irrespective of the particular polarities with which line S is energized, relay FP in the control omce and relay FP at the field station repeat the operations of relays F and F to effect the synchronous operation of the stepping relays in the control oflice and at the field stations.

Relay IV in the control oflice is picked up dur 7 ing the first off period by means of a circuit extending from front contact I4 of relay SA, backcontact 48 of relay FP, conductor I42, back contact 49 of relay VP, back contact 50 of relayZV and winding of relay 'IV, to Relay IV closes a stick circuit for itself extending from front contact I4 of relay SA, stick conductor 64, front contact 5| of relay IV and wind-. ing of relay IV, to 6 When relay IV is picked up, a circuit is com pleted for picking up relay E extending from back contact I9 of relay 3V, back contact 20 of' relay 2V,- front contact 2I of relay IV, back contact 34 of relay VP, conductor I43 and winding of 5.

' PP, conductor I42, front contact 49 of relay VP,

of relay 2V, front contact 51 of relay IV and winding of relay VP, to Relay VP establishes a stick circuit for itself extending from front contact 32 of relay SAP, conductor I45, front contact 58 of relay VP and over the remainder of the above described pick-up circuit, to the winding of relay VP. This stick circuit for relay VP is effective until relay 2V is picked up during the second off period, which opens back contact 56 included in the stick circuit.

For maintaining relay VP in its actuated condition after relay 2V is picked up during the second off period, an additional stick circuit is established extending from front contact 32 of relay SAP, back contact 52 of relay FF or back contact 59 of relay MBP or back contact 69 of relay MAP, one or more of which back contacts are closed during the off period and thence through conductor I46 and front contact 6| of relay VP, to the winding of relay VP.

'the circuit for picking up relay EP which has been previously described. This advances the system from the first on period into the second off period, since the actuation of relay EP opens its contact 21 and ole-energizes the S line, as well as the A and B lines.

This is the second off period. Relays F and FF are dropped and a circuit is established for picking up relay 2V extending from front contact I4 of relay SA, back contact 48 of relay back contact 62 of relay 3V, front contact 63 of relay IV and winding of relay 2V, to Relay 2V closes a stick circuit for itself by way of its front contact 65 to on stick conductor 64. A circuit is now closed for picking up relay E which extends from back contact I9 of relay 3V, front contact 20 of relay 2V, front contact 34 of relay VP, conductor I43 and winding of relay E to Relay E opens its back contact 33 allowing relay EP to drop and again energize line S at its back contact 21. This advances the system out of the second off period.

This is the second on period. Relays F and PP are again picked up and relay VP is dropped,

due to its pick-up and first stick circuit being open at back contact 56 of relay 2V and its second stick circuit being open at back contacts 52 of relay FP, 59 of relay MBP and 69 of relay MAP, all of these latter relays now being picked up. The circuit of relay E is now interrupted at front contact 34 of relay VP, allowing relay E to drop and establish the above described pick-up circuit for relay EP. Relay EP opens its back contact 21 which de-energizes the line conductors for advancing the system out of the second on period.

This is the third off period. Relays F and PP are again released and a circuit is established for picking up relay 3V extending from front contact I4 of relay SA, back contact 48 of relay FP, conductor I42, back contact 49 of relay VP, front contact 50 of relay 2V and winding of relay 3V, to Relay 3V establishes its stick circuit by way of its front contact 66 to on stick conductor 64. A circuit is now established for picking up relay E extending from front contact I9 of relay 3V, back contact 34 of relay VP, conductor I43 and winding of relay E, to Relay E opens its back contact 33 which drops relay EP and this in turn energizes line S by closing back contact 21, which is eifective to advance the system out of the third off period.

This is the third on period. Relays F and PP are again picked up and a circuit is established for picking up relay VP which extends from front contact 32 of relay SAP, front contact 52 of relay FP, front contact 53 of relay MBP, front contact 54 of relay MAP, conductor I44, front contact 55 of. relay 3V and winding of relay VP, to Relay VP again closes the above described stick circuit for itself, which extends through its front contact 58 and now includes front contact 55 of relay 3V. This sticks relay VP until the system advances through the change to normal period, when relays SA and SAP are dropped for interrupting all energized circuits to the winding of relay VP.

The circuit of relay E is now open at back contact 34 of relay VP and since relay 3V is picked up, the circuit through front contact 34 to relay E is interrupted. Relay E drops after a short time interval, causing relay EP to pick up and open line S at contact 21, which tie-energizes the line conductors and advances the system out of the third on period.

This is the change to normal period. Relays F and PP are dropped and it will be assumedthatrelay 3V is the last stepping relay of the series. Relay LV has been shown in this embodiment to indicate how additional stepping relays are connected in the circuit when required. Relay LV is also shown with back contacts 24 and I2! which are for a purpose which will be later described. It will be understood that the last stepping relay of the series is connected in a manner indicated by the connections of relay LV. If there are only three steps actually used in the system, then of course, relay LV would be omitted and contacts 24 and I21 would be placed on relay 3V.

Relay E cannot be picked up during this last off period because its pick-up circuits are open at points on relays 3V and VP above described. Relay EP can not be dropped at this time because relay E does not open its circuit at back contact 33. This results in relays F and FF remaining down for a suificient time to allow relay SA to drop, which opens its front contact I4 and allows all the stepping relays to be restored to normal, since is removed from stick con-1 ductor 64. Relay SA opens its front contact 3| which de-energizes relay SAP, allowing this latter relay to release and by opening its front contact 32 causes the release of relay VP. Relay SAP, in opening its front contact 32, also opens the circuit of relay EP which allows this relay to drop away.

When the last stepping relay of the series is picked up (assuming this to be relay LV), the stick circuit of relay C is interrupted at back contact 24 of vrelay LV and relay 0 is released. The release of relay SA interrupts the stick circuit of relay STR at its front contact I6, which allows relay STR to be restored to normal. After the release of relay STR, the S line conductor is de-energized and the A and B line conductors are energized with potential on the A line and potential on the B line, as indicated in the second partof the change to normal period. Relays MA, MB and their repeating relays MAP and MBP now pick up and thesystem is advanced into the normal period with line S de-energized, the A line conductor energized and the B line conductor energized I It has already been mentionedthat the stepping relays and the steering relays at the field stations operate in a manner similar to corresponding relays in the control oflice. and for this reason. it is not believed necessary to describe all the operating and pick-up circuits of these relays in detail. Relays IV 2V and 3V of Fig. 3 are picked up in synchronism with relays IV, 2V and'SV of Fig. 2A.

The pick-up circuits of the stepping relays shown in Fig. 3 extend from front contact I66 of relay SA back contact I61 of relay-FP (which operates in synchronism with relay F? in .the control ofiice), and front contact I68 of relay S0 during the transmission of control impulses; The extension of this circuit to the stepping relay Windings is through back and front contacts I69 of relay VPhwhich circuit is identical with that of Fig. 2A.

From the above description and by referring to the operation chart it will be observed that the stepping relays are picked up in rotation during successive off periods and the steering relays are shifted during the on periods. The steering relays VP and VP (and relays similar to VP at other stations) pick up during the odd on periods and release during the even on periods.

Contacts 59 and 60 of relays MBP and MAP of 'Fig.'2B connected in multiple with back contact 52 of relay FP, are for the purpose of preventing the release of relay VP during the evenon periods-until relays MBP and MAP are picked up. The purpose of contacts 53 and 54 of relays MBP and MAP in series with front contact 52 of relay FP, is to'insure that relays MBP and MAP are picked up at the beginning of the oddlon periods before relay VP can be picked up. These four contacts on relays MBP and MAP therefore serve the purpose of holding back the shifting of relay VP until the relays, which are to be conditioned over the line conductors, are properly positioned,

Duringv the change to normal period, the stepping relays and the steering relaysof Fig. 3 are released in a manner similar to those in the control office, when relay SA drops and opens its front contacts I66 and I13.

Relay VPC of Fig. 3 performs a function similar to that described in connection with contacts 53, 54, 59, and 60 of relays MAP and MBP in the control office. That is, this relay prevents the shifting of relay VF until the relays in the line conductors, have been properly conditioned. The 'stick circuit of relay VPkextending through its front contact 112 is not interrupted during an even on period until relay VPC picks up and opens its back contact I14. Relay VPC can not pick up until both the A, and B line impulsing relays PLA and PLB are down. Therefore, relay .VP cannot drop untilboth the A and. B line conductors are conditioned by relays PLA and PLB during the even on periods.

Furthermore, relay VP cannot be picked up during the :odd on periods until relay VPC picks up and closes its front contact I19 and relay VPC as above mentioned, cannot pick up until the A and B line conductors are conditioned by relays PLA and'PLB being down. This insures that the relays at the field station in the A and B line conductors'will be in their proper positions, as Well as the relay in the S line conductor before relay VP can be shifted. 7

It will be seen that during a control cycle, the end of the normal period is marked off by relay STR. picking up and energizing theline The start of the conditioning periodis marked off by relay STR picking'up and the end of the conditioning period is markedoif by the picking'up of relay EP. 7 Similarly, the end of each on period and the start of each of! period is marked off by the actuation of relay EP. The end of each off period and the beginning of each on period is marked off by the release of relay EP. The

, beginning of the change to normal off period is marked off by the picking up of relay EP and the end of this period is marked off by the energization'of the A and B lines exclusive of the stepping line, which is effective to pick up relays MA, MB, MAP and MBP.

During the transmission of indications, the

normal period, the off periods, the on pe-1 with the character of the code impulses, with lines.

A and B serving as the return conductors during the on periods. 'It will be recalled that in some cases, lines A and B in multiple form the return;

circuit and in other cases line A is opened so that line B alone supplies the return path for the impulses applied to line S. It will now be as,- sumed that the stepping relays in the control office and at the field station, together with the associated steering relays,'operate as above described and'an explanation will be given of the circuits which will be effective during this operation to transmit controls.

It will be recalled that line S is conditioned with a preliminary impulse for picking up relays similar to S0 at the field stations and during this conditioning period, relays SA and SAP in the control office and relay SA at the field station are actuated. Relays similar to SA at other field stations are likewise picked up.

It is assumed that the impulse applied to line S during the first on period is for actuat-. ing relay F of Fig. 3 to the right and-that thev A line conductor I I is energized for picking up relay FA The manner in which this combination a is determined in the control oflice has been explained. During the first on period, the impulse applied to line S and the energized condition of line A are executed at the field stations. The picked up position of relay FA (in cooperation with relay F positioned to the right) maintains the station relays similar to S0 operated, which have code jumpers associated with the first step connected to control bus similar to I64.

It has been assumed that the station shown in I Fig. 3 is the one to be selected and that all others At those stations having a jumper similar to I15 connected to bus similar' are dropped out.

to I64, relays similar to S0 will be maintained energized during the first on period, by means of a circuit similar to that extending from front contact I" of relay S0 back contact I6I of relay 3V back contact I62 of relay 2V front contact IE3 of relay IV jumper I15 in its full line position, bus I64, front contact I65 of relay FA contact I60 of relay F in its right hand position and winding of relay $0 to At those stations not having a jumper similar to I15 connected to the bus similar to I54, the relays similar to S0 are dropped because the above circuit is incomplete.

When the system advances into the second off period, those relays similar to S0 which are up will be stuck up over a circuit similar to that extending from front contact I'I'i of relay S0 front contact I58 of relay SA back contact 559 of relay FF, or make-before-break contact I66 of relay F in its de-energized position, in multiple with contact I59, and winding of relay SO to It is, of course obvious that the stick circuits of those relays similar to S0 which are dropped during the first on period are not complete during the second off period, since the above traced stick circuit is open at contacts similar to I11.

The system now advances into the second on period by means of a impulse in line S. Relay 2V is up and relay VP is down during this period and a circuit is completed for holding relay SO in its operated position, which extends from front contact ll? of relay S0 back contact I65 of relay 3V front contact I62 of relay 2V code jumper I86 in its full line position, bus lSE, back contact I82 of relay FA contact I of relay F! in its left hand position and winding of relay $0 to Relay FA is down at this time for closing its back contact I82 because the condition of line A is open as above pointed out and relay F is positioned to the left because of the impulse applied to line S.

It will be understood that in the embodiment disclosed herewith, only the relay S0 of Fig. 3 will be maintained energized during this period, since it is assumed that complete station selection is accomplished with two steps. With two stepping relays used for station selection, four stations may be selectively chosen by dropping out onehalf (2) of the stations on the first step which leaves two relays similar to S0 picked up. Then on the second step, one-half (1) of the remaining relays similar to S0 will be dropped, leaving only one (which is assumed to be relay S0 of Fig. 3) in its actuated position.

During the third off period, relay 3V is picked up and relay S0 is stuck up 'over the previously described circuit including its front contact I11 and make-before-break contact I60 of relay F in its deenergized position, in multiple with back contact I59 of relay FP As soon as relay 3V picks up, potential is connected through front contact II'I of relay S0 and front contact ISI of relay 3V to the winding of relay S0 so that this relay is maintained energized during the remainder of this cycle. With relay S0 stuck up after station selection, additional impulses are effective to operate only those stepping relays at the station illustrated in Fig. 3 since the circuit for these relays is by way of front contact I68 of relay S0 only at the station illustrated.

During the third on period, which takes place after station selection, the No. 3 control is executed by actuating relay F of Fig. 3 to the right and by deenergizing the A line conductor, which prevents the picking up of relay A circuit is now closed for actuating switch machine relay SMR to the right which extends from front contact ll? of relay S0 front contact IGI of relay 3V contact I60 of relay F in its right hand position, back contact I88 of relay LV front contact I83 of relay 3V and upper winding of relay SMR to With relay SMR positioned to the right, a circuit is closed from contact I84 of relay SMR in its right hand position and normal operating winding of switch machine 3M to (ON). This results in operating the switch machine in such a direction that switch TS is advanced to its normal locked position.

It will be understood that in the event of a impulse applied to line S during the third on period, relay F would be positioned to the left and the above described circuit would be by way of contact I68 of relay F actuated to the left, back contact 2i! of relay LV front contact 2E8 of relay 3V and lower winding of relay SMR to This would result in positioning relay SMR to the left and in closing its contact I85 at the left, the switch machine motor would be energized in the opposite manner for moving the track switch TS to the reverse locked position.

During the third on period, the second portion of the No. 3 control is executed by closing a circuit which extends from front contact 22I of relay S0 front contact 224 of relay FP contact 23%! of relay F in either position (this circuit being completed irrespective of the polarity in line S), back contact 229 of relay FA back contact 232 of relay LV front contact 233 of relay (W and lower winding of relay SR to This is effective to position relay SR to the left.

In the event that the second part of the No. 3 control is determined by relay PCA in Fig. 2B being down so that the A line conductor is energized for picking up relay FA then relay SR would be energized by way of its upper winding over a circuit which would extend from front contact 22I of relay S0 front contact 22 of relay FP contact 238 of relay F front contact 229 of relay FA back contact 234 of relay LV front contact 235 of relay 3V and upper winding of relay SR to In brief, the positioning of levers SML and SGL of Fig. 2A determines the polarity applied to the switch machine and signal relays SMR. and SR and these relays in turn govern the operation of the switch machine and signal devices. Obviously, if the control lever SML is moved to a position out of correspondence with the track switch TS this track switch will be operated but if the control lever is placed in a position which corresponds with the position of the track switch, then the track switch stays in its former position.

Under the heading Polarity selection of impulses it was explained how the four distinctive code combinations for each step are obtained. It has been pointed out above how the first one of these combinations is effective, by way of jumper H5 connected to bus I64, to maintain relay S0 in its actuated position during the first on period. The second one of these combinations requires jumper I15 to be in connection with bus 231 to hold relay S0 since relay F would be actuated to the right and relay FA would be down for this combination. The circuit of relay S0 would then be through back contact I of relay FA and contact I68 of relay F in its right hand position.

For the third combination jumper I15 would have to be connected to bus 238 to hold relay 50 since relay F would be actuated to the left and relay FA would be up. The circuit of relay S0 would then be through front see of relay F1 in its left hand position.

It will thus be obvious how relays similar to S0 are selectively controlled on a choice of four combinations per step basis, by maintaining only those relays picked up at the stations where the code jumper i115 matches the polarity of energization of the line S, as well as the energized or deenergized condition of line A. A similar selection is made by means of code jumper I80 on the second step.

After station selection, the selective stick circult of relay S0 is switched from jumpers I15 and I 80 to front contact I6I of relay 3V which holds relay S0 until the end of the cycle at which timerelay 3V releases. The potential on front contact IBI of relay 3V is extended to the selective contact I60 of relay F so that selection is by way of the'two channel circuits including front contacts I83 and 2I8 of relay 3V during the third step and front contacts I88 and 2 I! of relay LV when morethan three steps are provided. These two channel circuits constitute a means controlled by relay F for selectively positioning one two-position relay such as'SMR at each step. Two additional channel circuits controlled by relay FA have potential applied to them through contacts 229 of this relay and include contacts 232, 233, 234 and 235 of relays 3V and LV and lead torelays such as relay SR so that these relays may each be actuated to either one of two positions during each step. 2

Although the detailed circuits of the signal relays or other control devices have not been shown, it will be understood that they function to complete circuits for operating the signal devices. Also; the step-by-step operation of the stepping relays may occur in sequence and in synchronism for as many steps as required to transmit controls to such other signal relays or devices as desired.

The transmission of controls as above explained in detail may be briefly understood by considering 50 that the code sending relays 'PC, NC and PC A are preconditioned during each off period, for determining the character of the code impulse to be applied to the line conductors during the succeeding on period. The character of such succeeding impulse is recorded by means of. the

polar magnetic stick type relay? and the neutral. type relay FA The recorded impulse is executed at the field station during the succeeding on period by'conditioning relays similar to S0 during station selection and by positioning particular function control relays such as relays SMR. and SR at the selected station after station selection.

' This transmission of controls continues until the predetermined number of steps have been taken wluch, by way of example, has been specifically illustrated as including three steps, two of which have been employed for station selection followed bya single step which is employed for the-transmission of the particular controls after station selection;

End of control. cycZe.-It has been explained that relays F, FP, SA and SAP and all stepping relays in the control office are released during the change to normal period which follows the T likewise interrupts the stick circuit of relay third on period. It will be recalled that the change to normal" period is long compared with other off periods resulting in relays F and FF in the control ofiice and relays F and FF at the field station being down for a time interval sufiio 'cient to allow relays SA, SAP and SA to be released. The stepping relays and the associated steering or half step relay at the field station release when relay SA drops and opens its contacts I65 and H3. The stick circuit of relay S0 including its front contact I", is interrupted when relay 3V drops and opens its front contact IGI and since relays F FP and SA are down at this up during the cycle, is released so that the next code-determining relay in order may be effective at the beginning of the next cycle, if its corresponding starting button has been actuated and this condition stored by a storing relay.

Automatic start by a field station.With the system in a normal period or period of blank, it may be initiated into a cycle of operations from a field station, either in response to some automatic change in traffic conditions or in response to the operation of a traffic controlling device,

resulting from the transmission of controls from the control office during a control cycle, when such a device assumes a new position. For example, track switch T8 may be shifted from a normal to a reverse position in response 40 to a control transmitted by lever SML, in a manner previously described. When the track switch responds to such a control it causes a relay (not shown) to momentarily interrupt the stick circuit of a change relay CHP of Fig. 3. Similarly; track relay T may be released by a change in traffic conditions caused by a train passing over the associated detector track circuit, in accordance with the usual practice. The release of relay 5O CHP in a manner which is well known. In brief, the stick circuit for relay CHP is carried through front and back contacts of relay T. This stick circuit may similarly be carried through like contacts of other controlling devices at the field station. 2

Irrespective of the particular change which occurs, it results in dropping the change repeating relay CHP which closes a pick-up circuit for relay PLA extending from back contact 236 ofrelay FP back contact I56 of relay SA back contact I51 of relay CI-IP and lower winding of relay PLA to Relay PLA closes a stick circuit for itself extending from back contact I93 of relay SA front contact I89 of relay PLA and lower winding of relay PLA to The actuation of relay PLA opens its back contact I90 which allows relay VPC 'to release. Relay PLA also opens the A line conductor I I at its back contact I50 which results in dropping relays MA, MB, MAP and MBP in the control ofiice.

Referring to the indication cycle portion of Fig. 4, the system is now in the first part of the initiating period with all three line conductors I deenergized as indicated by reference character 75 0 (open) associated with all three lines. The release of relay MAP closes a circuit for picking up relay FC extending from ba'ck contact 69 of relay SAP, back contact 'IZof relay STR, back contact 10 of relay MAP and winding of relay FC, to Relay FC prevents the picking up of relay C during this cycle by opening its circuit at back contact 23 of relay FC.

Relay FC closes a circuit for picking up relay STR which extends from back contact 32 of relay SAP, front contact I3 of relay FC and winding of relay STR, to- Relay FC also closes a stick circuit for itself extending from back contact I2'I of relay LV, conductor I47, front contact I9 of relay FC and winding of relay FC, to Relay FC also closes a circuit for picking up relay NC extending from front contact I5 of relay FC, back contact I4 of relay C and lower winding of relay NC, to

Since this is a cycle for the transmission 0 indications, all of the impulses applied to line S are because relay NC is held in its picked up position throughout the cycle over the above described circuit. The operation of relays NC and STR close a circuit for energizing line S with potential, which extends from the terminal of battery B, back contact 8 of relay PC, front contact 26 of relay NC, winding of relay F and back contact 21 of relay EP to line S. The return path extends through the line relays at the field stations, resistance coils R and. R at the last field station, back contacts of relays such as PLB at other field stations, conductor I52, back contact I53 of relay PLB B line conductor I 2, winding of relay MB, conductor I24, front contact I of relay NC, back contact 25 of relay PC and front contact I0 of relay STR, to the terminal of battery B.

The circuit branches at resistance coil R and leads through relays such as relay FA at other stations, back contacts such as PLA at other stations, conductor I5I, winding of relay FA front contact I50 of relay PLA lower winding of lock-out relay L0 back contact I9I of relay SA B line conductor I2, winding of relay MB, conductor I24, front contact 'I of relay NC, back contact 25 of relay PC and front contact I0 of relay STR, to the terminal of battery 13.

It will be noted from the above traced circuit that the A line conductor II is open toward the control ofiice, at back contact I50 of relay PLA at the station initiating the call. The A line conductor I5I, extending toward stations farther away from the control office, is connected to the B line conductor at the station initiating the call, through the lower winding of relay L0 The resistance coils R and R provide a sufficient drop in the A and B line conductors extending from the station shown in Fig. 3 to the end of the line, so that the lower winding of relay L0 is not sufficiently shunted to prevent its operating.

With the system in the second part of the initiating period, line S energized line A extending to the control oilice deenergized and line B energized relays MB and MBP in the control oflice are picked up and relays F and F are positioned to the left. Relays F3? in the control ofiice and FF at the field station are picked up over circuits closed by contacts 29 and I54 of relays F and F respectively in their left hand dotted positions. Relay L0 is picked up by the current flowing in line conductor I5I over the circuit above described. Relay FA also picks up but is ineffective at this time.

The system is now in the look-out period. Re-

Relay SA at the field station is picked up over a circuit completed at front contact I55 of relay FP With relays FP or SA up, no other relay similar to PLA can be picked up, because the pickup circuit is open at back contacts similar to I56 or 236. Relay SA closes a stick circuit for relay L0 extending from front contact I93 of relay SA front contact I94 and upper winding of relay L0 to Ihe picking up of relay SA opens the pick-up circuit of relay PLA at back contact I56 and the stick circuit of relay PLA at back contact I93 so that relay PLA is dropped.

The system is now advanced into the conditioning period. The A line conductor is energized due to the current in conductor I5I throughback contact I50 of relay PLA A line conductor II, winding of relay MA; conductor I6, back contact I5 of relay PCA, front contact I3 of relay STR,

front contact 1 of relay NC, back contact 25 of relay PC and front contact I 0 of relay STR, to the terminal of battery B. As shown in the oper ation chart during the conditioning period, line S isenergized and lines A and B are energized Relays MA and MAP in Fig. 2D pick upwhen the A line is energized during this period and relay MAP establishes a stick circuit, for itself extending from on stick conductor 54, back contact 11 of relay E, front contact and upper Winding of relay MAP, to Relay SAP is picked; up when relay SA closes its front contact 3|. Relay VPC of Fig. 3 is again picked up when relay PLA releases, by the closure of its back contact I90. Relay EP of Fig. 2B is picked up during the conditioning period over a circuit extending from front contact 32 ofrelay SAP, back contact 33 of relay E and lower Winding of relay EP, to Relay EP opens the S line conductor at its back contact 21, which deenergizes the three line conductors 28, II and I2 to advance the system out of the conditioning period.

This is. the first off period. The stepping relays and their associated steering relays in the control office and at the field stations are operated in synchronism during an indication cycle in the same manner as previously described in connection with a control cycle, so that the detailed description of this operation will not be repeated. The line conductor S is impulsed by relay EP in the same manner as previously described, so that the detailed description of this operation will not be repeated. The relays simistored office and field start conditions, the com-v munication system functions to send alternate controls and indications on separate cycles of operation. Before proceeding with the detailed description of the circuit operations under this condition, a brief summary will be given of the functioning of the system when aplurality of 

